This invention relates, in general, to semiconductor wafer processing, and more particularly, to methods and structures for thin film formation.
Chemical vapor deposition (CVD) is a very versatile and widely used process in the semiconductor industry to form thin films on semiconductor and insulating substrates. Such thin films include insulative, semiconductive, and conductive materials. CVD is defined as the formation of a non-volatile solid film on a substrate by the reaction of vapor phase chemicals (reactants) that contain the necessary constituents. The reactant gases are introduced into a reaction chamber and subsequently decomposed and reacted at a heated surface to form the thin film.
Current CVD reactor designs all share the same basic components including a reaction chamber, a substrate support structure (i.e., a susceptor), an energy source, gas sources, and devices for controlling gas flow, pressure, and temperature. In a typical CVD process, the following steps occur: a) a given composition of (and flow rate of) reactant gases and diluent carrier gases is introduced into the reaction chamber; b) the gas species move to the substrate; c) the reactants are absorbed on the substrate; d) the absorbed reactants undergo migration and film-forming chemical reactions; and e) the gaseous by-products of the reactions are desorbed and removed from the reaction chamber.
In view of the above steps, the gas flow characteristics within the reaction chamber significantly affect a CVD process and reactor performance. For example, in current CVD reactor designs, turbulence in the flow of reaction gases caused by reactor chamber geometrical constraints as well as current susceptor designs inhibit efficiency and uniformity of the deposition process and promotes the deposition and migration of contaminants within the reaction chamber. Moreover, existing designs are such that gas flow characteristics are indeterminate (i.e., difficult to predict) due to geometrical constraints, flow introduction methods, and susceptor motion.
In addition to using inefficiently designed reactors, CVD process users typically place the wafers to be processed in regions of the reaction chamber where non-uniform flow velocities exist. Also, CVD process users tend to place the substrates in regions of the reaction chamber where interactions with boundary layers formed at the reaction chamber wall occur. Moreover, some CVD reactor designs spin the substrate(s) while the CVD process takes place thereby creating turbulence and spiral vortices. The above practices contribute to turbulence, particle generation, thicker boundary layers, and lower mass transport.
Furthermore, current CVD reactors introduce both the source gases and the carrier gas as mainstream gases well upstream from the substrates. This creates an inefficient and costly deposition process because excess source gases must be introduced into the reactor chamber to assure that sufficient reactants reach the substrates. This also degrades process control.
Based on the above and other deficiencies associated with the prior art, structures and methods are needed for improving gas flow characteristics and reactor efficiency in CVD processing.